When we first discovered the structure of DNA, it looked like all of life's mysteries were at our fingertips. We could control life and death! But soon enough, we started to run up against the limits of our awesome power over genetics — and one of the harshest taunts comes from the simple tortoiseshell cat.

In the early days of genetics, society had a pie-eyed optimism about the power it would soon wield. We thought everything about a creature could be catalogued in one string of information. This data could be translated, switched out, copied, and duplicated at will. It was just a matter of gathering enough information. We were wrong.

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Genetics has thrown us for a loop over and over. Mutations, junk genes, extreme variation, and epigenetics have made it very clear that nothing was as easy as it first appeared. One of the most interesting limits of cloning is exemplified by the housecat. Some pets are clonable — and there have been businesses set up for just that — but tortoiseshell cats cannot be replicated, because part of their genes simply aren't there anymore.

Tortoiseshell cats are the result of two different genes teaming up. One gene will turn the cat red, a nice solid ginger. The other will make it a black cat. Each gene is inherited from one of the tortoiseshell's parents. Each is on one of the tortie's X chromosomes. The tortoiseshell look is produced because of a process called ‘X-linked inactivation.' The cells of developing embryo of the tortoiseshell cat randomly shut off one of the X chromosomes. And there's no general consensus among the cells about which one to switch off, so each cell simply picks one. This random shut-off is why tortoiseshells have an unpatterned mix of black and red hair over their bodies.

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Cloning a tortoiseshell involves taking the DNA from one cell. Since each of the cells have only one active X chromosome, when a new tortoiseshell embryo is developing using the borrowed DNA, it only has one gene affecting its coloration.

Thus, a cloned tortoiseshell kitten will generally be either black or red. Even if someone were to nab a cell from a developing embryo before the X-linked inactivation happened, the new cloned kitten would also randomly inactivate its X chromosomes, leaving two cloned siblings that don't have the exact same color pattern. No matter how advanced the technology, there is no way to clone a certain kind of animal. Life is sometimes determined to be unique, in spite of our best efforts to make it predictable.